1. Field of the Invention
This invention relates to a lamp reflector having an aluminum-deposited mirror surface particularly suitable for headlights, fog lights, etc. mounted on motorcycles, automobiles and other vehicles. More particularly, it relates to a lamp reflector having a substrate made by injection molding a bulk molding compound (hereinafter abbreviated as BMC) comprising a matrix resin mainly comprising an unsaturated polyester resin and glass fiber as an inorganic filler. The matrix resin comprises an unsaturated polyester, a polymerizable compound having a polymerizable double bond in the molecule thereof which serves as a crosslinking agent for curing the unsaturated polyester, and a thermoplastic resin which serves for controlling cure shrinkage of the unsaturated polyester.
2. Description of the Related Art
In the field of lamp reflectors for use in headlights and fog lights of vehicles, it is well known to use a substrate formed by injection molding a BMC comprising a matrix resin mainly comprising an unsaturated polyester resin and inorganic fillers, such as glass fiber (a reinforcing material), particulate fillers, and whiskers. The substrate made from a BMC is known for dimensional stability (molding precision as designed with reduced influences of heat shrinkage), heat resistance, rigidity, and economy.
However, containing reinforcing fillers such as glass fiber and whiskers, a BMC is heavy, having a specific gravity of 1.8 to 2.1, which is almost double that of general thermoplastic resin molding materials. So are lamp reflectors obtained therefrom. Heavy lamp reflectors result in increased fuel consumption of vehicles, which does not meet the recent social demand for energy saving.
The present inventors sought for possibility of reducing the weight of BMC molded parts while retaining their main characteristics except economy, such as dimensional stability, heat resistance and rigidity. They noted that glass fiber used in a BMC is a reinforcing component indispensable for retaining the main characteristics of a BMC molded part, whereas inorganic fillers other than glass fiber are not so contributory as glass fiber to secure the main characteristics and are not seen as indispensable. It was confirmed that replacing part of an inorganic filler other than glass fiber with hollow glass spheres (glass balloons filled with gas and having a small specific gravity) made a good effect on BMC weight reduction.
However, use of hollow glass spheres in a BMC gave rise to a new problem that the glass spheres are collapsed under shearing force applied in injection molding, resulting in a short shot, a failure to achieve sufficient weight reduction, or a reduction in rigidity.